The invention claimed and disclosed herein pertains to disk array systems and apparatus for supporting disk drives in a disk array system, and particularly to methods and apparatus to reduce the effects of shock and vibration on disk drives in a disk array system.
Disk array systems include several (typically 10-30) disk drives, which are supported in a support apparatus. The support apparatus also supports components, which service the disk arrays. Such support components can include power supplies, cooling fans, and data controllers to control the flow of data to and from the disk drives. FIG. 1 depicts a front elevation view of typical prior art disk array system 10. The disk array system includes an outer enclosure 12, which is supported on a surface xe2x80x9cSxe2x80x9d (such as a floor or the like). The outer enclosure 12 serves as a general protective enclosure to protect the other components of the disk array, and also acts to seal the disk array system to improve the flow of cooling air circulating within the enclosure 12. The outer enclosure 12 also includes a front door panel, which is not shown in this view to facilitate the viewing of the other components of the disk array system 10.
Located within the outer enclosure 12 of the disk array system 10 is a support frame 14, which is commonly fabricated from metal angle sections and the like. The support frame 14 includes trays 16. Each tray 16 serves to support a chassis, only one of which is shown as chassis 18. The chassis 18 defines a plurality of openings 24A, 24B, 24C, 24D and 24E. Each opening 24A-E is configured to receive an operational component of the disk array system 10. In the example depicted, openings 24A and 24B are depicted as receiving respective disk drives 20A and 20B. The disk drives can be secured within the chassis openings using latches 22 or the like. Located behind the trays 16 is a back plane 30 which includes electrical connectors 28 and 34, allowing the functional components to be put into signal and electrical communication with other functional components within the disk array system 10.
Turning to FIG. 2, the prior art disk array system 10 of FIG. 1 is depicted in a side elevation sectional view. As can be seen, the back plane 30 allows the disk drive 20A to be connected to the electrical connector 28. The back plane 30 can further include connectors 28A and 34A, allowing flexible cables (not shown) to be used to interconnect the various functional components of the disk array system 10. As can be seen in this view, the disk drive 20A includes a data storage disk section 38 which can be accessed by a read-write head (not shown) which is supported on disk arm 36, allowing data to be transferred to and from the disk section 38.
A common problem encountered with disk array systems is that of shock and vibration, which can affect the performance of individual disk drives with a disk array system. For example, when a disk drive receives a mechanical force in the way of a shock or vibration, the disk arm 36 and the disk section 38 (FIG. 2) can be temporarily misaligned. This can result in a data read/write error, requiring the disk array system to re-read or rewrite the data sector affected by the misalignment. This in turn affects the operational efficiency of the disk array system, resulting in slower data access times. In severe cases mechanical shock and vibration to the disk drive can cause physical damage to the disk drive, requiring that the disk drive be removed for servicing or replacement.
The sources of mechanical shock and vibration which can affect a disk drive originate from three primary sources. The first source is forces external to the disk array system. These can include shock or vibration transmitted through the surface upon which the disk array system is mounted (such as surface xe2x80x9cSxe2x80x9d in FIG. 1), and can result from earthquakes and even persons walking on the surface. Another source of external shock is via the external housing (12 of FIG. 1), as for example when a person bumps against the housing. The second source of mechanical shock and vibration is from self-excitation. That is, since the disk section (38 of FIG. 2) rotates essentially continuously at a very high speed, a natural frequency inherent to the disk drive itself results. Depending upon the mass of the disk drive and the manner in which the disk drive is supported within the chassis (18 of FIG. 1), these self-excitation forces may be resonant, which can cause severe operational problems with the disk drive. The third primary source of mechanical shock and vibration, which can be imparted to a disk drive, is random excitation, which can be transmitted to the disk drive from other functional components within the disk array system, such as other disk drives and cooling fans. The most common source of this excitation is movement of the arms that support the read/write heads inside the hard disk drives.
Turning to FIGS. 3A and 3B, schematic diagrams depict how sources of shock and vibration can affect a disk drive in a disk array system. FIG. 3A depicts the translational effects that shock and vibration can have on a disk drive 20 mounted within a chassis 18, which is in turn supported by a frame 14. Shock and vibration can cause the disk drive to move in directions A1 and A2, which can be in any of the X, Y or Z directions. Self-excitation of the disk drive 20 can be dampened by resistive elements R1 and R2 interposed between the disk drive 20 and the chassis 18, but can be compounded by compliant elements C1 and C2. Likewise, random excitation forces imparted to the chassis 18 can be filtered by resistive elements R1 and R2, but can be amplified by compliant elements C1 and C2. External sources of shock and vibration imparted to the frame 14 can be attenuated by resistive element R3 interposed between the frame 14 and the chassis 18, but again can be amplified in a resonant setting by compliant element C3.
Turning to FIG. 3B, a second effect of shock and vibration on the disk drive 20 is depicted. In this figure the effects are not translational movement, but rotational movement of the disk drive 20 in directions T1 and T2, which can be about any of the three rotational (X, Y or Y) axes. Likewise, the chassis 18 can also experience such rotational movement as the result of the various sources of shock and vibration. As with the translational forces depicted in FIG. 3A, the self-excitation forces of the disk drive 20 of FIG. 3B which tend to produce rotational movement of the disk drive 20 can be resisted by resistive elements R4, but can also be amplified in a resonant setting by compliant elements C4. Likewise, random excitation forces, as well as external forces, can cause rotational movement of the chassis 18, which can be attenuated by resistive elements R5, but potentially amplified by compliant elements C5. In certain settings, the compliant elements C4 and C5 can act together to set up a resonance, resulting in severe translational and rotational movement of the disk drive 20, as well as the chassis 18.
The resistive elements R1-R5 of FIGS. 3A and 3B can be, for example, a sheet of rubber material placed between the disk drive 20 and the chassis 18, or between the chassis and the frame 14. The compliant elements C1-C4 of FIGS. 3A and 3B can be, for example, rubberized or otherwise elastically deformable components disposed between the disk drive 20 and the chassis 18, and between the chassis and the frame 14. Such elastically deformable components can also include resistive characteristics, and can thus provide both compliant and resistive (i.e., dampening) characteristics. As one example of a compliant element, it is a common practice to dispose a deformable spring steel leaf spring between the chassis 14 and a disk drive 20 to allow the disk drive to be held in a relatively fixed position with respect to the chassis, while also allowing the disk drive to be easily removed from the chassis for service or replacement. Such a leaf spring is primarily a compliant component, although it also has certain internal resistance to deformation.
One prior art solution to the problem of shock and vibration on a disk drive in a disk array system is to isolate each disk drive in the system by placing a rubber material between the disk drive and the chassis. While this is of some help in isolating the individual disk drive from forces external to the disk array system, as well as random excitation forces, it does nothing to alleviate the effects of self-excitation. In fact, mounting the disk drive in such a manner can contribute to reduced performance, since the disk drive will be somewhat free to move with respect to the chassis as a result of the self excitation forces. In order to reduce self-excitation of disk drives, manufacturers of such devices can manufacture the disk drives to exacting specifications, using very close tolerances and precisely balanced components to reduce self-excitation of the disk drive. However, such manufacturing techniques generally tend to increase the cost of disk drives.
What is needed then is a disk array system, and a method of providing a disk array system, which attenuates the effects of shock and vibration on disk drives within the system, yet avoids the shortcomings and detriments associated with prior art methods and/or devices.
The present invention provides methods and apparatus to reduce vibration, and the effects thereof, in disk drives in a disk array system. In one embodiment, disk drives in a disk array system are rigidly connected to one another such that the effective inertial mass of each disk drive now becomes the total or collective inertial mass of all disk drives rigidly connected to one another within the disk array. The increase in the effective inertial mass of each disk drive helps attenuate the resulting movement of each disk drive as a result of general external forces, internal forces resulting from resonant self-excitation (e.g., the spinning of the disk), and internal forces resulting from random self-excitation (e.g., the movement of the read-write arm). Further, by rigidly connecting disk drives to one another within the disk array, the effects of self-excitation of each disk drive tend to be attenuated by or reduced by the effects of self-excitation of the other disk drives, which are rigidly connected to one another. In one variation of the present invention disk drives within a disk array are directly connected to one another in a rigid manner such that the collective (effective) inertial mass of each disk drive becomes the collective inertial mass of all disk drives thus connected. In another variation of the present invention the disk drives are individually rigidly connected to a cage (and thus effectively to one-another), such that the effective inertial mass of each disk drive becomes the collective inertial mass of all disk drives connected to the cage, as well as the inertial mass of the cage itself. Further, the disk drives can be rigidly connected to prior art components of a disk array (such as a chassis and/or a frame used to support the disk drives in the disk array), in which case the effective inertial mass of each disk drive becomes the collective inertial mass of all disk drives connected to the component(s) of the disk array, as well as the inertial mass of such components.